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Abstract:

Abstract. The flow of glaciers and ice streams is strongly influenced by the presence of water at the interface between ice and bed. In this paper, a hydrological model evaluating the subglacial water pressure is developed with the final aim of estimating the sliding velocities of glaciers. The global model fully couples the subglacial hydrology and the ice dynamics through a water-dependent friction law. The hydrological part of the model follows a double continuum approach which relies on the use of porous layers to compute water heads in inefficient and efficient drainage systems. This method has the advantage of a relatively low computational cost that would allow its application to large ice bodies such as Greenland or Antarctica ice streams. The hydrological model has been implemented in the finite element code Elmer/Ice, which simultaneously computes the ice flow. Herein, we present an application to the Haut Glacier d'Arolla for which we have a large number of observations, making it well suited to the purpose of validating both the hydrology and ice flow model components. The selection of hydrological, under-determined parameters from a wide range of values is guided by comparison of the model results with available glacier observations. Once this selection has been performed, the coupling between subglacial hydrology and ice dynamics is undertaken throughout a melt season. Results indicate that this new modelling approach for subglacial hydrology is able to reproduce the broad temporal and spatial patterns of the observed subglacial hydrological system. Furthermore, the coupling with the ice dynamics shows good agreement with the observed spring speed-up.

Abstract: The Correct Derivation Of Paleotemperatures From Ice Cores Requires Exact Knowledge Of All Processes Involved Before And After The Deposition Of Snow And The Subsequent Formation Of Ice. At The Antarctic Deep Ice Core Drilling Site Dome C, A Unique Data Set Of Daily Precipitation Amount, Type, And Stable Water Isotope Ratios Is Available That Enables Us To Study In Detail Atmospheric Processes That Influence The Stable Water Isotope Ratio Of Precipitation. Meteorological Data From Both Automatic Weather Station And A Mesoscale Atmospheric Model Were Used To Investigate How Different Atmospheric Flow Patterns Determine The Precipitation Parameters. A Classification Of Synoptic Situations That Cause Precipitation At Dome C Was Established And, Together With Back-trajectory Calculations, Was Utilized To Estimate Moisture Source Areas. With The Resulting Source Area Conditions (Wind Speed, Sea Surface Temperature, And Relative Humidity) As Input, The Precipitation Stable Isotopic Composition Was Modeled Using The So-called Mixed Cloud Isotope Model (Mcim). The Model Generally Underestimates The Depletion Of 18o In Precipitation, Which Was Not Improved By Using Condensation Temperature Rather Than Inversion Temperature. Contrary To The Assumption Widely Used In Ice Core Studies, A More Northern Moisture Source Does Not Necessarily Mean Stronger Isotopic Fractionation. This Is Due To The Fact That Snowfall Events At Dome C Are Often Associated With Warm Air Advection Due To Amplification Of Planetary Waves, Which Considerably Increases The Site Temperature And Thus Reduces The Temperature Difference Between Source Area And Deposition Site. In Addition, No Correlation Was Found Between Relative Humidity At The Moisture Source And The Deuterium Excess In Precipitation. The Significant Difference In The Isotopic Signal Of Hoarfrost And Diamond Dust Was Shown To Disappear After Removal Of Seasonality. This Study Confirms The Results Of An Earlier Study Carried Out At Dome Fuji With A Shorter Data Set Using The Same Methods.